Why hate?

Today on my way from the office I was confronted by a man who was standing in my way on the side walk. We did the "which way do I go" dance until I realized that he was trying to get in my way, and he was waving his hands and trying to look through my sun glasses.
Annoyed at this point, I flipped him the bird. To which he responded "see I knew you could see," disgusted I said "see I knew you were ignorant." He then looked at me blankly, and I turned and walked away.

But why, why did he have to take time out of his day to do that? What need did that full fill for him?

I really just don't understand hate, I don't get it.

Counting down the days until I am out of this mall minded city... DC here I come...